A Phase III Randomized, Multicenter, Two Arm, Open-label Trial to Evaluate the Efficacy of Trastuzumab Emtansine Compared With Treatment of Physician's Choice in Patients With HER2-positive Metastatic Breast Cancer Who Have Received at Least Two Prior Regimens of HER2 Directed Therapy

This randomized, multicenter, 2-arm, open-label study (TH3RESA) will evaluate the efficacy and safety of trastuzumab emtansine (T-DM1) in comparison with treatment of the physician's choice in participants with metastatic or unresectable locally advanced/recurrent human epidermal growth factor receptor 2 (HER2)-positive breast cancer. Eligible participants will be randomized to receive either trastuzumab emtansine 3.6 mg/kg intravenously every 21 days or treatment of the physician's choice. Participants continue to receive study treatment until disease progression or unacceptable toxicity occurs. This study is also known under Roche study protocol number BO25734.